Katie Hopkins is smiling at the photographer with the trademark grin that convinced TV viewers of her super-confidence before she walked out on Sir Alan Sugar during the 2007 Apprentice final. She then scandalously left her husband and the father of her two children for a married man. Then she reappeared in the Australian jungle on I'm A Celebrity... and next month, the 34-year-old mother of three is standing as an independent MEP in the European elections.

Nothing, it seems, would surprise us about Katie, except perhaps one thing - the revelation that she suffers from epilepsy, a condition that saw her thrown out of the Army.

Confidential: Katie Hopkins has kept her illness a secret since her first attack at 18

Her illness started suddenly, yet subtly, when she was 18.

Chatting with friends at sixth-form college in Barnstaple, Devon, she suddenly stopped talking and stared into space. After an uncomfortable silence, her friends nudged her, but she looked at them vacantly.

'I knew something had happened but I had no idea where I went,' says Katie.

But then the blank spells started to happen more frequently. 'I would be talking and lapse into silence, or I would be walking down the street and suddenly stand still for several seconds,' she says. 'I would reassure people that nothing was wrong, that I was deep in thought about something.'

Until now, Katie, who runs a management consultancy, has kept her condition from everyone except her parents, Roy and Anona, both 60 and retired farmers, her partner Mark Cross, 45, a graphic designer, and close friends and colleagues.

But she has chosen to speak out about the condition, which affects 450,000 people in the UK, to coincide with National Epilepsy Week, which starts on May 17.

'People are frightened of epilepsy as they imagine someone thrashing on the floor foaming at the mouth. Even my parents are not used to the idea of my having epilepsy. My mum won't even say the word, preferring to call it my "little dizzies".

'I have hidden my condition for so long but it is time people knew how common it is and why it is nothing to fear.'

While one in 20 of us will experience a seizure at some point in our lives, every epilepsy case is individual, with some born with it and others developing it later in life, after traumas such as a blow to the head or a brain infection such as meningitis or stroke.

Why Katie developed it in her late teens remains a mystery to doctors but by the time she was studying for a degree in politics and economics at Exeter University she was having up to 15 blank spells - known medically as absences - per day.

She was referred by her GP to consultant neurologist Professor Adam Zeman, at the Royal Devon & Exeter Hospital.

There she underwent tests including an electroencephalogram (EEG) where electrodes were attached to her scalp and a computer recorded her brain's electrical signals.

'The doctors could see abnormalities in the front temporal lobe of my brain,' she says.

'The results were devastating as I know people take the mickey out of epilepsy. In your teens you want to blend in and be one of the group, so I would act super-confident as a way of compensating for it.'

Katie Hopkins pictured with her mother Anona at Sandhurst

Katie was put on medication to control the seizures but she hated the side effects of nausea and dizziness so stopped taking them.

'I didn't realise epilepsy treatment is not an exact science and it takes experimentation to find the right dose, but I decided just to live with it and carry on with all the lies.'

Without revealing her secret, Katie completed her degree and at 21 won a place at the Royal Military Academy at Sandhurst in Berkshire.

However, on her application form she omitted to reveal her seizures.

'I didn't want a few fits to stop me achieving my dream so I didn't lie, I just didn't tell them,' she says.

But in the closed confines of military life she was unable to hide her condition from her superiors.

'One day, we were drilling, carrying guns and I had an absence, wandering off in totally the wrong direction. I was hauled out by my drill sergeant. I told him I felt dizzy but I knew they were suspicious,' she says.

Then a few weeks later, while on holiday with friends in Devon, she suffered her first major 'tonic-clonic' seizure - a violent convulsion involving the momentary loss of consciousness, leaving the sufferer with no memory of the incident. Katie's convulsions were so violent she broke a vertebra in her upper back.

'I came round thinking I must have had a bad fit as my back was in agony. Hospital X-rays revealed the muscles had spasmed so hard I had broken my back by just lying in bed.'

She was out of action for several weeks, but once again lied to her Army colleagues that she had taken a bad fall. Indeed, Katie even managed to pass her final military exams with flying colours.

But a suspicious Army medic requested permission to see her GP's medical records which Katie knew would reveal the truth - and would mean instant dismissal from the Army.

Katie says: 'On my last night at Sandhurst, just before the big passing-out ball, I was marched in to see the senior medical officer. He told me that when everyone else removed the cover from the pips on their uniforms at midnight to show they had officially passed out, I was not to remove mine. And that was how I found out.'

The shock perhaps prompted two other tonic-clonic seizures soon after and Katie decided to seek medical treatment again.

Katie Hopkins, second from left in back row, with fellow Apprentice contestants and Alan Sugar

In 1997, during three days of tests at the Royal Devon & Exeter Hospital, her brain was again wired up to an EEG machine, with a video camera which recorded her seizures.

'It was a grim experience, particularly as I was put on a mental-health ward full of confused people.'

To suppress the absences and convulsions she was put on medication that has been constantly reviewed over the years as doctors try out new drugs and dosage levels.

She currently takes medication twice a day and has a stash in every handbag, gym kit and briefcase and makes sure it is the first thing she packs on business trips or holidays.

The side effects such as mouth ulcers, sleepiness and headaches, she says, are worth it to lead as normal a life as possible.

But while daytime seizures have mostly been under control for the past nine years, she has suffered sleep seizures which occur as she falls into and emerges from a deep sleep.

'Mark is woken up by me shaking and shouting out "Well done!" or "Great" or "It'll be OK!" Luckily it is always positive things,' she laughs.

'After a few seconds I come round but often I have fallen out of bed. And I usually bite the sides of my tongue while I fit which is painful and causes ulcers. I haven't had a full night's sleep in years as a result.'

During the 11 weeks she spent living in The Apprentice house, she did not tell the other candidates. When she had to share a bunk bed, she dismissed her seizures as nightmares.

'I thought they might have looked at me differently or been too worried to give me a high-powered job.'

When later that year she took part in I'm A Celebrity..., round-the-clock filming forced her to tell the producers about her condition and she was banned from sleeping in a hammock for safety reasons.

But epilepsy has not prevented Katie from becoming a mother of three. She had India, four, and Poppy, three, with her former husband Damian McKinney, and in November gave birth to Max with Mark.

But her first, unplanned pregnancy was fraught as for the first two months she was taking a high dosage of drugs.

'I panicked that they may have harmed my baby. We had several anxious months but luckily, India was born perfectly healthy,' she says.

When she became pregnant with Poppy, Katie cut her medication - although this brought on another tonic-clonic seizure. However, Poppy and Max were born without complications.

Similar to most epilepsy sufferers, Katie is desperate to lead a life without seizures and is even considering having part of her brain removed in a radical operation.

The procedure involves surgeons removing a section of skull then attaching electrodes to parts of the brain and transmitting shockwaves through them to see which cells are not operating properly.

The malfunctioning part of the brain can then be removed, but only if it is not responsible for a vital function such as mobility or language.

Despite the obvious risks, Professor John Duncan at the London's National Hospital of Neurology, where the procedures are carried out, claims epilepsy surgery halves seizures in 90 per cent of cases, with 20 per cent of patients seeing their seizures stop altogether.

'In the 700 operations we have carried out since 1999, only one person ended up with more seizures,' says Professor Duncan.

Katie is still deliberating, believing the risk of losing her speech or mobility too high.

'If I didn't have three children and Mark to consider, I would not hesitate.'

For now, Katie will deal with the effects of daily medication. 'It gets me down. I would like to be normal and not have to worry. But it could be worse, I could have daily convulsions,' she says.

'I have always acted confidently to over-compensate for my condition but I still cannot reconcile me, Katie, with this person who has epilepsy - and I don't know if I ever will.'

• www.epilepsy.org.uk, www.katiehopkins.co.uk.

450,000 sufferers - and 75 new cases every day

A seizure, or fit, is caused by a sudden burst of excess electrical activity in the brain, causing a temporary disruption in the message passing between brain cells. The brain messages are then mixed up or disrupted.

There is no proven cause but medics believe that every brain is capable of producing a seizure. A brain tumour, blow to the head, a stroke or a brain infection are all possible causes of fitting.

There is no cure, but most types of seizures can be controlled by medication.

75 people are diagnosed with epilepsy daily.

450,000 people in the UK suffer from epilepsy.

There are more than 1,000 epileptic-related deaths each year from the consequences of falling down or from sudden unexpected death in epilepsy (SUDEP), where the nerves to the heart and lungs shut down during a seizure.

Types of seizures vary from mild absences, where the person remains conscious, to the dramatic tonic-clonics, where the person has convulsions, loses consciousness and has no memory of the attack.